Is it safe and helpful to take magnesium during pregnancy?

At ordinary supplement doses no clear harm has been shown, and no clear benefit for the baby either. A Cochrane review of 10 trials with 9,090 pregnant women found oral magnesium made no significant difference to stillbirth and newborn death, to babies born small, or to pre-eclampsia. Its authors concluded there is not enough high-quality evidence that it is beneficial. Two later trials of 300 mg magnesium citrate a day in Brazil, in 829 and 290 women, found the same.

Myth. Magnesium tablets do not make a pregnancy go better for the baby. In the largest recent trial, 829 women with at least one risk factor took 300 mg of magnesium citrate a day from mid-pregnancy to delivery. Problems for the baby came to 18.4 percent on magnesium and 18.0 percent on placebo.

What the trials found

Mother and baby

The Cochrane review is the widest view. Its 10 trials gave doses from 128 mg to 1000 mg in different salts, and only 2 of them were rated high quality. Across the trials, the risk ratio for stillbirth and newborn death was 1.10 (95% CI 0.72 to 1.67), for a small-for-gestational-age baby 0.76 (0.54 to 1.07), and for pre-eclampsia 0.87 (0.58 to 1.32). All three intervals cross 1.0, which means no clear effect either way. Among secondary outcomes the review saw a possible rise in newborn deaths before hospital discharge (RR 2.21, 95% CI 1.02 to 4.75). It came mostly from one trial with many severe birth defects in the magnesium group, and it disappeared when those deaths were left out.

One result did stand out. Women taking magnesium were 35 percent less likely to be admitted to hospital during pregnancy (RR 0.65, 95% CI 0.48 to 0.86), in 3 trials with 1,158 women. The abstract does not give how many women that was in absolute terms. An umbrella review of 16 meta-analyses later rated this as one of only 2 of 55 magnesium outcomes with strong evidence, but it rests on those same 3 trials.

Unsettled. Pre-eclampsia is where the reviews disagree. A 2022 meta-analysis of 7 trials with 2,653 women found 24 percent less pre-eclampsia on oral magnesium (RR 0.76, 95% CI 0.59 to 0.98), an interval that only just stays below 1.0. The Cochrane estimate on fewer trials crossed 1.0. In women at normal risk the 2022 review itself found no clear effect (RR 0.91, 95% CI 0.67 to 1.25). The drop came from trials that also enrolled high-risk women. A 2020 trial in 290 low-income Brazilian women found pre-eclampsia in 18.1 percent on magnesium and 19.7 percent on placebo, a difference that was not significant. The 2022 review does not give the absolute numbers behind its 24 percent.

Leg cramps

This is the reason many women are told to try magnesium, and the answer is unclear. A 2021 meta-analysis of 4 trials with 332 pregnant women found cramp frequency was not reduced (WMD -0.47, 95% CI -1.14 to 0.20). A 2020 Cochrane review of 8 small trials with 576 women could not pool them and concluded it is unclear whether any treatment works for leg cramps in pregnancy. One 4-week trial of 300 mg magnesium bisglycinate in 80 women with frequent cramps did find a benefit: cramps were at least halved in 86.0 percent on magnesium against 60.5 percent on placebo. It is a single positive trial and the pooled analyses do not back it.

Gestational diabetes

In women with gestational diabetes who were not on insulin, 5 small trials with 266 women found magnesium lowered fasting blood sugar by 7.33 mg/dL. The confidence interval reported for that, 7.02 to 7.64, is implausibly narrow for trials that small. Preterm birth (OR 0.42, 95% CI 0.06 to 2.95) and very large babies (OR 0.34, 0.08 to 1.35) did not change clearly. A better blood sugar number has not been shown to mean a better pregnancy.

Who should be careful

Not for everyone. If your kidneys do not work well, magnesium supplements are a question for your doctor before you start. According to NIH, the risk of magnesium toxicity rises with impaired kidney function or kidney failure, because the body loses the ability to clear the excess. This matters in pregnancy with kidney disease, and when pre-eclampsia affects the kidneys.

The NIH upper limit for magnesium from supplements is 350 mg a day for adults. Magnesium in food does not count toward it. The same 350 mg applies in pregnancy, though that figure sits in a table we could not quote. The two Brazilian trials and the cramp trial used 300 mg a day.

Magnesium sulfate given by drip in hospital is a different thing from a tablet. It is a medicine used under monitoring for women at risk of very early birth. In a 2026 Cochrane review it caused maternal side effects severe enough to stop treatment about three times as often as the comparison (RR 3.21, 95% CI 1.88 to 5.48, 3 trials, 4,736 women). Results from that treatment say nothing about a supplement, in either direction.

What expert bodies say

The Cochrane authors say there is not enough high-quality evidence to show that magnesium supplementation in pregnancy is beneficial. The NIH Office of Dietary Supplements sets the upper limit for supplemental magnesium at 350 mg a day for adults and warns about poor kidney function. We could not retrieve the World Health Organization antenatal care recommendation on leg cramps, so it is not used here.

How we searched

What would change this answer

• A fresh Cochrane update. The current one searched to March 2013, and the later Brazilian trials were both null, so an update could close the question or reopen it.
• A large trial of oral magnesium for pre-eclampsia in women at high risk. The 2022 review's result sits right on the edge, and the trials behind it are not large enough to tell which women it applies to.
• One well-run trial for leg cramps with a shared way of measuring them. The Cochrane reviewers could not pool eight trials because each counted cramps differently.
• Trials of gestational diabetes that report what happens to the baby with enough women to show it.

The rest of the nutrient, including how much you need and which foods carry it, is in the magnesium guide.

Sources

1. ev-mgpg-01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 9090
   In the analysis of all trials, oral magnesium supplementation compared to no magnesium was associated with no significant difference in perinatal mortality (stillbirth and neonatal death prior to discharge) (risk ratio (RR) 1.10; 95% confidence interval (CI) 0.72 to 1.67; five trials, 5903 infants), small-for-gestational age (RR 0.76; 95% CI 0.54 to 1.07; three trials, 1291 infants), or pre-eclampsia (RR 0.87; 95% CI 0.58 to 1.32; three trials, 1042 women).
   
   Who: pregnant women in randomized and quasi-randomized trials of oral magnesium supplements vs placebo or no treatment
   Effect: perinatal mortality RR 1.10 (95% CI 0.72 to 1.67; 5 trials, 5903 infants); small-for-gestational age RR 0.76 (0.54 to 1.07; 3 trials, 1291); pre-eclampsia RR 0.87 (0.58 to 1.32; 3 trials, 1042 women)
   Certainty: Only 2 of 10 trials high quality; doses and salts varied widely (128 mg to 1000 mg).
   Cochrane Database Syst Rev, 2014 · checked 2026-10-06 · we read the abstract
2. ev-mgpg-02 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 1158
   Women receiving magnesium were significantly less likely to require hospitalisation during pregnancy (RR 0.65, 95% CI 0.48 to 0.86; three trials, 1158 women).
   
   Who: pregnant women in randomized trials of oral magnesium supplementation
   Effect: hospitalization during pregnancy RR 0.65 (95% CI 0.48 to 0.86); also fewer Apgar <7 at 5 min (RR 0.34, 4 trials, 1083 infants)
   Certainty: Secondary outcome; when restricted to the two high-quality trials no primary outcome differed.
   Cochrane Database Syst Rev, 2014 · checked 2026-10-06 · we read the abstract
3. ev-mgpg-03 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized trials · n = 9090
   There is not enough high-quality evidence to show that dietary magnesium supplementation during pregnancy is beneficial.
   
   Who: pregnant women in 10 randomized trials
   Effect: no benefit shown on primary outcomes; possible excess neonatal death (RR 2.21, 95% CI 1.02 to 4.75) driven by one trial with congenital anomalies, disappearing when those deaths were excluded
   Certainty: Review searched to March 2013; later RCTs (BRAMAG 2020) also null.
   Cochrane Database Syst Rev, 2014 · checked 2026-10-06 · we read the abstract
4. ev-mgpg-04 · Meta-analysis or systematic review · meta-analysis of randomized controlled trials · n = 2653
   Pooled results showed that oral magnesium supplementation during pregnancy significantly reduced the risk of preeclampsia (risk ratio [RR]: 0.76, 95% confidence interval [CI]: 0.59 to 0.98, P = 0.04) with no significant heterogeneity (P for Cochrane's Q test = 0.42, I2 = 1%).
   
   Who: pregnant women in randomized controlled trials of oral magnesium supplementation
   Effect: pre-eclampsia RR 0.76 (95% CI 0.59 to 0.98); normal-risk women RR 0.91 (0.67 to 1.25); mixed normal and high-risk RR 0.54 (0.35 to 0.83); severe pre-eclampsia RR 0.54 (0.18 to 1.69)
   Certainty: Borderline overall result; contrasts with the null Cochrane estimate (RR 0.87).
   Biol Trace Elem Res, 2022 · checked 2026-10-06 · we read the abstract
5. ev-mgpg-05 · Randomized controlled trial(s) · multicenter double-masked placebo-controlled randomized trial · n = 829
   The perinatal composite outcome occurred among 75 (18.4%) in the magnesium arm and 76 (18.0%) in the placebo group - an adjusted odds ratio (aOR) of 1.10 (95% CI 0.72-1.68).
   
   Who: women with a singleton pregnancy and at least one risk factor (prior preterm birth or preeclampsia, chronic hypertension, pre-pregnancy diabetes, age over 35, high BMI), northeastern Brazil
   Effect: perinatal composite 18.4% vs 18.0%, aOR 1.10 (95% CI 0.72 to 1.68); maternal composite 12.0% vs 9.7%, aOR 1.29 (0.83 to 2.00)
   Certainty: Largest recent RCT; 300 mg magnesium citrate from 12-20 weeks to delivery.
   BMC Pregnancy Childbirth, 2020 · checked 2026-10-06 · we read the abstract
6. ev-mgpg-06 · Randomized controlled trial(s) · randomized double-blind placebo-controlled trial · n = 290
   55/290 (18.9%) of pregnant women developed preeclampsia; 26/143 (18.1%) in magnesium group and 29/147 (19.7%) in the control group; OR 0.90 (CI 95% 0.48-1.69), p = 0.747.
   
   Who: low-income, low-risk pregnant women in Brazil enrolled at 12-20 weeks
   Effect: pre-eclampsia 26/143 (18.1%) vs 29/147 (19.7%); OR 0.90 (95% CI 0.48 to 1.69)
   Certainty: Women with high serum magnesium excluded before randomization; 28 lost to follow-up.
   BMC Pregnancy Childbirth, 2020 · checked 2026-10-06 · we read the abstract
7. ev-mgpg-07 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 332
   The frequency of leg cramps after treatment was not decreased in the treatment group compared to the control group (WMD = -0.47, 95% CI: -1.14-0.20, P = 0.167).
   
   Who: pregnant women with leg cramps in randomized controlled trials
   Effect: cramp frequency WMD -0.47 (95% CI -1.14 to 0.20); recovery OR 0.47 (0.14 to 1.52); side effects OR 1.82 (0.90 to 3.69)
   Certainty: Small trials; Cochrane 2020 could not pool and rated certainty low to very low.
   Taiwan J Obstet Gynecol, 2021 · checked 2026-10-06 · we read the abstract
8. ev-mgpg-08 · Meta-analysis or systematic review · Cochrane systematic review of randomized controlled trials · n = 576
   It is unclear from the evidence reviewed whether any of the interventions provide an effective treatment for leg cramps.
   
   Who: pregnant women with leg cramps in randomized controlled trials
   Effect: magnesium results inconsistent across single trials (e.g. never cramping RR 5.66, 95% CI 1.35 to 23.68, 69 women); low or very low certainty; no pooling possible
   Certainty: Outcomes measured in incomparable ways; safety could not be assessed beyond side effects.
   Cochrane Database Syst Rev, 2020 · checked 2026-10-06 · we read the abstract
9. ev-mgpg-09 · Randomized controlled trial(s) · double-blinded randomized placebo-controlled trial · n = 80
   Fifty per cent reduction of cramp frequency was significantly higher in the magnesium group than the placebo group (86.0% vs. 60.5%, P=0.007).
   
   Who: healthy pregnant women at 14-34 weeks with leg cramps at least twice a week
   Effect: 50% reduction in cramp frequency 86.0% vs 60.5% (P=0.007); 50% reduction in intensity 69.8% vs 48.8% (P=0.048); no difference in nausea or diarrhea
   Certainty: Single positive trial; pooled analyses are null.
   Matern Child Nutr, 2015 · checked 2026-10-06 · we read the abstract
10. ev-mgpg-10 · Meta-analysis or systematic review · systematic review and meta-analysis of randomized controlled trials · n = 266
    Overall, compared with control intervention for gestational diabetes, magnesium supplementation was able to significantly decrease FPG (MD = -7.33 mg/dL; 95 % CI = -7.64 to -7.02 mg/dL; P < 0.00001) and HOMA-IR (MD = -0.99; 95 % CI = -1.76 to -0.22; P = 0.01), but resulted in no obvious impact on serum insulin (MD = -4.17 μIU/mL; 95 % CI = -8.49 to 0.14 μIU/mL; P = 0.06), preterm delivery (OR = 0.42; 95 % CI = 0.06 to 2.95; P = 0.38), macrosomia (OR = 0.34; 95 % CI = 0.08 to 1.35; P = 0.13) or BMI change (MD = -0.01 kg/m2; 95 % CI = -0.06 to 0.04 kg/m2; P = 0.63).
    
    Who: women with gestational diabetes not on insulin, randomized controlled trials
    Effect: fasting glucose MD -7.33 mg/dL (95% CI -7.64 to -7.02); HOMA-IR MD -0.99; preterm delivery OR 0.42 (0.06 to 2.95); macrosomia OR 0.34 (0.08 to 1.35)
    Certainty: Very small trials; implausibly narrow CI for glucose; no effect shown on pregnancy outcomes.
    Eur J Obstet Gynecol Reprod Biol, 2024 · checked 2026-10-06 · we read the abstract
11. ev-mgpg-11 · Meta-analysis or systematic review · umbrella review of systematic reviews and meta-analyses · n = 16 meta-analyses
    Strong evidence according to the GRADE suggests that Mg supplementation can decrease the risk of hospitalization in pregnant women and reduce the intensity/frequency of migraine.
    
    Who: participants in meta-analyses of magnesium RCTs (16 meta-analyses, 55 outcomes)
    Effect: strong evidence (GRADE high, p<0.005) for decreased hospitalization in pregnancy and fewer migraine relapses
    Certainty: Rests on the same Cochrane outcome as ev-mgpg-02 (3 trials).
    Eur J Nutr, 2020 · checked 2026-10-06 · we read the abstract
12. ev-mgpg-12 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis of randomized controlled trials · n = 5917 women, 6759 fetuses
    However, magnesium sulphate probably increased maternal adverse effects severe enough to stop treatment (average RR 3.21, 95% CI 1.88 to 5.48; 3 RCTs, 4736 women; moderate-certainty evidence).
    
    Who: women at risk of preterm birth before 34 weeks given magnesium sulfate for fetal neuroprotection
    Effect: cerebral palsy RR 0.71 (95% CI 0.57 to 0.89), NNTB 60; maternal adverse effects stopping treatment RR 3.21 (1.88 to 5.48), moderate certainty
    Certainty: A medical treatment given by drip under monitoring, not a dietary supplement; included because readers conflate the two.
    Cochrane Database Syst Rev, 2026 · checked 2026-10-06 · we read the abstract
13. ev-mgpg-13 · Position of an expert body · agency fact sheet
    The Tolerable Upper Intake Level for supplemental magnesium is 350 mg for adults, and it ranges from 65 to 350 mg for children and adolescents, depending on age.
    
    Who: adults, including pregnant women (UL table applies from 19 years)
    Effect: UL 350 mg/day supplemental magnesium; food magnesium does not count toward the limit
    Certainty: Pregnancy-specific UL is the same 350 mg in the ODS table (table, not quotable).
    NIH Office of Dietary Supplements, Magnesium Fact Sheet for Health Professionals · checked 2026-10-06 · we read the section
14. ev-mgpg-14 · Position of an expert body · agency fact sheet
    The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost
    
    Who: people with impaired renal function or kidney failure
    Effect: raised risk of hypermagnesemia with reduced renal clearance
    Certainty: Relevant in pregnancy with kidney disease or pre-eclampsia affecting the kidneys.
    NIH Office of Dietary Supplements, Magnesium Fact Sheet for Health Professionals · checked 2026-10-06 · we read the section